1. Field of the Disclosure
The present application relates to a liquid crystal display device adapted to detect a bonding defect when a driver IC (Integrated Circuit) chip and a flexible printed circuit board are bonded in a display panel.
2. Description of the Related Art
Recently, display devices, such as liquid crystal display (LCD) devices, electroluminescent display (ELD) devices, and plasma display panels, have attracted public attention due to having features of high speed response, lower power consumption and superior color reproductivity. Such display devices are being used in a variety of electrical appliances, including television receivers, computer monitors, notebook computers, mobile phones, display portions of refrigerators, personal digital assistants, automated teller machines and so on. Also, customer demands are increasing for the display devices having an input device which can be easily and simply manipulated and can minimize operational errors. To meet the increasing customer demand, a touch screen panel is proposed which allows a user to input information by directly touching the screen with his finger or a touch pen.
Small display devices include driver IC chips which are directly disposed in a pad region of a display panel in one of a COG (chip-on-glass) format and a COF (chip on film) format. The driver IC chip includes one of a gate driver circuit and a data driver circuit.
Also, signals applied from an external system to the display panel are transferred to the driver IC chips on the display panel through a flexible printed circuit board (“FPCB” or “FPC”). To this end, the flexible printed circuit board is mounted to the display panel through a FOG (FPCB-on-glass) procedure to be connected to pads formed in the display panel.
FIG. 1 is a planar view showing the structure of a display device according to the related art. FIG. 2 is a planar view illustrating a method of testing for a bonding defect in a dummy pad when a flexible printed circuit board is mounted on a display panel of the related art.
Referring to FIGS. 1 and 2, the display device includes a display panel 10, a driver IC chip DIC and a flexible printed circuit board FPC. The display panel 10 includes an active area AA 20 used to display images. The driver IC chip DIC and the flexible printed circuit board FPC are mounted on a pad area 30 of the display panel 10. Also, the driver IC chip DIC includes a gate driver circuit (not shown), a data driver circuit (not shown) and a controller (not shown). The flexible printed circuit board FPC is used to transfer supply voltages, drive signals and data signals from an external system to the display panel 10.
The flexible printed circuit board FPC is mounted in a FOG region within the pad area 30 of the display panel 10. In order to inspect a bonding defect of the flexible printed circuit board FPC, dummy pads DUMMY PAD are formed on the FOG region of the display panel 10, and bonding resistance is measured from test points TP on the flexible printed circuit board FPC in which signal patterns connected to the dummy pads are formed. Such a connection configuration is also applied to another region of the display panel 10, in which the driver IC chip DIC is mounted, in the same manner. In other words, the dummy pads are also formed on another region of the display panel 10, which includes the driver IC chip DIC, and are connected to the test points TP on the flexible printed circuit board FPC, even though it is not shown in the drawings. As such, the driver IC chips DIC adhered to a COG region within the pad area of the display panel 10 by a COG procedure can be inspected for a bonding defect.
Also, the dummy pads DUMMY PAD, which are used to measure the bonding resistances of the driver IC chip DIC and the flexible printed circuit board FPC, are electrically connected to one another by a connection pattern formed on the COG region and the FOG region, respectively, of the display panel 10. As such, the resistance of a bonding portion can be obtained from the test points TP formed on the flexible printed circuit board FPC.
Meanwhile, a microscope can be used to inspect a bonded state of the driver IC chip, which are bonded through the COG procedure, and a bonded state of the flexible printed circuit board which is bonded through the FOG procedure. However, the microscopic inspection leads to not only decreased accuracy but also a longer inspection time.
The bonding resistance measurement can be more accurate than the microscopic inspection. However, the bonding resistance measurement requires forming the test points TP using the dummy pads and bringing resistance probes in contact with the test points, for each display panel. Due to this, the bonding resistance measurement leads to a longer inspection time than the microscopic inspection.